Servo brake mechanism for vehicles



P 1941- G. R. G. GATES 2,254,998

'SERVO BRAKE MECHANISM FOR VEHICLES Filed- Feb. 7, 1940 3 SheetsSheet l Sept. 2, 1941. G. R. -G..GA'I ES- 2,254,993

SERVO BRAKE MECHANISMTOR VEHICLES Filed Feb '7, 1940 3 Shets-Sheet 2 G.R.c..GA1- s INVEIVT'GR A rv' P 1941.- G. R. G. GATES 2,254,998

I SERVO BRAKE MECHANISM FOR VEHICLES Filed Feb. 7, 1940 3 Sheets-Sheet 3 612.6. GA-res In v aw TOR' Patented Sept. 2, 1941 SERVO BRAKE MECHANISM FOR VEHICLES Geoffrey Robert Greenbergh Gates, London, England, assignor of one-half to Automotive Products Company Limited, London, England Application February '7, 1940; SerialNo.

In Great Britain February 20,1939 e 6 Claims. 101. 188-152) This invention'relates to servo brake mechanism for vehicles, of the type in which energy for operating the brakes is derived from some part of the power transmission system of .the vehicle which rotates with the driven road wheels or with the engine, through a torque-applying unit comprising a part (hereinafter referred to as "the driving part) rotating continuously with the power transmission system,'and a part (hereinafter referred to as the driven part") which incorporating the invention; and may be frictionally engaged with the continu- Figure 4 is a diagram illustrating an alternaously rotating part through the actuation, by the tive method of returning the cam member to its driver of the vehicle or another operator of 2. initial position. pedal, hand-lever or other control (hereinafter r In the torque applying unit shown'in Figures referred to as the drivers control) to apply a 1 and 2, the driving part comprises a set of discs torque to the braking system which is employed It, splined at If to the enlarged end l2 of a shaft to operate the brakes. I3 driven from the gearbox of a motor road ve- The object of the present invention is to prohicle, the discs It being arrangedin alternate sevide an improved arrangement for converting quence with a second set of discs I4 of larger the torque applied to the driven part of the torque radius forming the driven part of the unit. The applying unit into a linear pull or thrust on a discs I! are carried by rods I5 arranged parallel brake rod or on a piston of a liquid pressure with the driving shaft i3 and radially outwards master cylinder. v of the periphery of the discs It, the rods l5 being According to the invention, the driven part of mounted in an end member l6 itself mounted on the torque pp ying unit carries a symmetrical a ball thrust bearing II in the housing I8. At face cam member, and a brake operating rod carthe opposite end of the pack of discs l0, I4 isa ries a follower engaging the cam normally at one cap member 2| also carried by the rods IS, the point on its axis of symmetry, the arrangement cap member 2| receiving the pressure applied to b in S h hat rotary mov m n f h driven engage the two sets of discs, such pressure being part of the torque applying unit in either direcapplied by means of a plunger 22 mounted vin a t on app s a linear force t the b ak p ating cylinder 23 co-axial with the shaft It, the plunger rod, the force app ed t0 t e ake Ope at g rod being moved by liquid pressure generated in a being always in the same direction. master cylinder 24 (Figure 3) operated by the Accordin to another asp t f the v nti n. foot pedal 25 which constitutes the driver's servo brake mechanism for vehicles of the type tr l; referred to and c mpri n Symmetrical cam The end member It comprises a circular plate rotat n with the driven part of the to que app yof greater radius than the discs l4, and a cylinin unit, and a brake operating rod carrying a drical sleeve 26 is formed integrally with the follower which norma ly engages the cam at One 4 plate about its edge, one end of the sleeve 26 point on its axis of symmetry, i cha a is d being perpendicular to the driving shaft l3 of by t e feature that the com is a face cam the unit, whilst the sleeve is of greater length at centric with the axis of the t q pp y -v one end of a diameter than at the other so that The cam member preferably comprises a cylinits other end forms a cam surface 27 inclined to drical sleeve having one end face oblique to the the driving shaft l3. A plunger 28 mounted in axis of the torque applying unit, and the otherv the housing I8 carries a' roller 3| engaging the end f e perpendicular o e Said S- The P pe pendicular end surface of the cam sleeve 26, pendicular face of the cam member may be en the plunger 28 being adjustable by means of a gaged by a roll r p vc lly mounted in the housstud 32 and lock-nut 33 to vary the position of -ing of the torque applying unit, to transmit the load in the brake rod to the housing and avoid the application of side loads to the bearings of the unit.

The invention is hereinafter described with reference to the accompanying drawin s, in which:

Figure 1 is a vertical section through the torque applying unit of a servo brake mechanism according to the invention:

Figure 2 is a plan view of the unit shown in Figure 1, tion;

Figure 3 is a diagram of a servo brake system the roller. is mounted A liquid pressure master cylinder 34 on the housing l8 at the side of the cam 25 opposite to the roller-carrying plunger 28, the axis of the master cylinder being in line with that of the plunger 28, and a thrust rod parts of the unit beingshown in sec- T engaging the piston of the master cylinder 34 carries at'its end a second roller 33 engaging the inclined cam surface 21. To the pivot of the roller 33 on the thrust rod 35 is connected a guiding arm 31, Figure 2, pivoted at 33 in the housing It, and movable in a planetangential to the cam sleeve 23 at the point of engagement of the roller 33. The arm 31 constrains the thrust rod 35 to move sothat the roller 33 follows an arc of a circle about the pivot 33 of the guiding arm, and cannot move to any substantial degree away from the common axis of the master cylinder 34 and the fixed plunger 28 carrying the supporting roller. The guiding arm at is extended beyond its pivot 38 to engage a piston 4i in an auxiliary cylinder 42 carried by the housing l8, the cylinder 42 being in communication with the pedaloperated master cylinder 24. The piston 4| is acted on the cylinder 42, and the arm 31 ,is so arranged that as the thrust rod 35 moves to apply the brakes the arm is moved away from the piston, allowing it to move outwardly under the pressure generated by the master cylinder 24.

When the pedal 25 is depressed by the driver, liquid is forced from the pedal-operated master cylinder 24 into the cylinder 23, and .the discs of the torque-applying unit are brought into engagement. The end member l3 carrying the cam -sleeve 23 is thuscaused to turn,'and the roller 33 on the thrust rod 35, which normally engages r the lowest point of the caml surface 21, is moved away from the fixed roller 3| as the cam sleeve turns,

ment of the rod 35, which in turn moves the thu's'causing substantially linear movepiston of the master cylinder 34 mounted on the torque applying unit, to forceliquid into wheel cylinders 44 (Figure 3) which spread the shoes of the vehicle brakes. The reaction in the thrust rod 33 is transmitted through the cam sleeve 23 by a spring 43 tending to urge it into gravity. This tendency assisted by the return force on the master cylinder piston returns the cam to its initial position. Alternatively, the cam sleeve may be brought back to its initial position by spring means, as shown in Figuredv for example, a chain 45 being attached at one end to the end member l3, and passing over a pulley 43 to'an anchorage 41 on a plate.43 rotatably mounted in the housing i8 and having secured to it one end of a clock spring 3|, the other end of which is anchored to the housing itself. The spring 3| tends to rotate the plate 43 and apply a ull to the chain 45, which thus tends to take up a position in which the part between the end member 13 and the pulley 43 extends radially. The cam sleeve and end member are thus always returned to this position by the spring 3|. 5

By the present invention there is provided a torque applying unit for a servo brake mechanism which is very compact and simple to manufacture, and in which no side loads are borne by the bearings of the unit.

What I claim is:

1. Servo brake mechanism for vehicles comprising a shaft rotating with the driven road wheels of the vehicle, a rotatable disc, disconnectible friction coupling means between the shaft and the disc, a symmetrical falce cam formed on one face of the disc, brakes on said vehicle, a. brake operating rod coupled to said brakes, a follower on said brake operating rod engaging the face cam whereby movement of the rod to apply, the brakes is produced when the friction coupling means are engaged, a circumferential track on the opposite face of the a disc, said traick being of substantially equal diamto the fixed roller 3| and there is consequently no side load on the bearings of the torque applyi -u The control system forthe torque applying unit is designed according to the specification I or my British Patent No. 4:17.173 m which the application of the brakes by the unit automatically reduces the engaging pressure on the discs of the unit, the reduction of pressure being carried out in the cylinder 42. The movement'of the arm '31 as the brakes are applied allows the piston 4| to move out of the cylinder 42 and increase the volume of the cylinder, so that for a given degree of depression of the brake pedal 23 the pressure engaging the discs .is decreased when the brakes are operated until a state of balance is set up, thus ensuring that the brakes are always under full control ofthe operator.

when the brakes are: to be released, the operator releases the pedal 25 and relieves the preseter to the face cam and lying in a plane perpendicular to the axis of the disc, and a roller mounted on fixed bearings and engaging the circumferential track, the cam follower and roller engaging the face cam and circumferential track respectively at points substantially on a common radius of the disc, whereby the disc is supported by theroller against the reaction in the brake operating rod.

v 2. Servo brake mechanism for vehicles comprising a shaft rotating with the driven road wheels of the vehicle, a rotatable sleeve mounted with its'axis horizontal and having one end oblique to the axis of the sleeve to form a symmetrical face cam, and the other end perpendicular to said axis, disconnectible friction coupling means between the shaft and the sleeve, brakes on the vehicle, a brake operating rod coupled to said brakes, a follower on said brake operating rod engaging the face cam vertically above sure on the discs of the torque-applying unit,

thus allowing the cam sleeve 23 to be returned I to its initial position and allowing the master cylinder piston to return and permit the return of liquid from the wheel cylinders 44. The pulloff springs in the brakes, acting through the column of liquid, and the customary return spring in the master cylinder itself, together produce a'lcad tending to return the piston. By arrangingthe cam sleeve so that in its initial position the axis of symmetry of the cam surface 21 is vertical, and the deepest part of the sleeve 23 is'at the bottom,

it is given a natural tendency ,to returntc that position under the force ofthe axis of the sleeve, whereby movement of the rod to apply the brakes is produced when the. friction coupling means are engaged, and a roller mounted in fixed bearings and engaging the perpendicular end of the sleeve in the same radial plane as the cam follower to support the sleeve against the reactionin-the brake operating rod, whereby the action of gravity on the sleeve tending to maintain the deepest, part thereof at the bottom acts to return said mecha'nis'm'to the inoperative position.

3. Servo :brake mechanism for vehicles comprising a shaft rotating with the driven road wheels of the vehicle, a rotatable disc, disconnectible friction coupling means between the shaft and the disc, a symmetrical face cam formed on one face of the disc, brakes on said vehicle, a brake operating rod coupled to said brakes, a follower on said brake operating rod' engaging the face cam whereby movement of the rod to apply the brakes is produced when the friction coupling means are engaged, a chain attached to said disc, a spring coupled to the other end of the chain, a pulley mounted in fixed bearings over which the chain passes whereby the spring acts to return the disc to a position in which that end of the chain adjacent its attachment to the disc extends radially outwardly, a circumferential track on the opposite face of thedisc, said track being of substantially equal diameter to the face cam and lying in a plane perpendicular to the axis of the disc, and a roller mounted in fixed bearings and engaging the circumferential track, the cam follower and roller engaging the face cam and circumferential track respectively at points substantially 'on a common radius of the disc, whereby the disc is supported by the roller against the reaction in the brake operating rod.

4. Servo brake mechanism for vehicles comprising a shaft rotating with the driven road wheels of the vehicle, a rotatable disc, disconnectible friction coupling means between the master cylinder is produced when the friction coupling means are engaged, a circumferential track on the opposite face of the disc, said track being of substantially equal diameter to the face cam and lying in a plane perpendicular to the axis of the disc, anda roller mounted in fixed bearings and engaging the circumferential track,

the cam follower and roller engaging the face cam and circumferential track respectively at points substantially on a common radius of the with its axis horizontal and having one end oblique to the axis of the sleeve to forma symmetrical face cam, and the other end perpendicupendicular end of the sleeve in the same radial plane as the cam follower to support the sleeve against the reaction in the brake operating rod, whereby the action of gravity on the sleeve tending to maintain the deepest part thereof at the bottom acts to return said mechanism to the inoperative position.

6. Servo brake mechanism for vehicles comprising a shaft rotating with the driven road wheels of the vehicle, a rotatable disc, disconnectible friction coupling means between the shaft and the disc, a symmetrical face cam formed on one face of the disc, brakes on said vehicle, a brake operating rod coupled to said brakes, a follower on said brake operating rod engaging the face cam whereby movement of the rod to apply the brakes is produced when the friction coupling means are engaged, an arm.

pivotally connected to the brake operating rod adjacent the cam follower, and lying in a plane substantially tangential to the cam member at the point of engagement of the follower, a fixed pivot for the arm, a liquid pressure master cylinder, a driver's control for operating said master cylinder, a motor cylinder connected to said master cylinder and controlling the friction coupling means, a compensating cylinder, and a piston in the compensating cylinder engaged by the arm, the arrangement being such that the movement of said arm as the brakes are applied permits the piston to move outwardly in the compensating cylinder and increase the spacein the cy1in-.

der, thereby decreasing the pressure acting to maintain the friction coupling means in engagement.

GEOFFREY ROBERT GREENBERGH GATES. 

